1. Field of the Invention
This invention relates to transmitting and receiving antennas, and, in particular, to antennas employing contrawound windings.
2. Background Information
U.S. Pat. Nos. 5,442,369; and 6,028,558, which are incorporated by reference herein, disclose Contrawound Toroidal Helical Antennas (CTHAs). See, also, U.S. Pat. Nos. 5,734,353; 5,952,978; 6,204,821; 6,218,998; 6,239,760; and 6,300,920.
A CTHA employs a toroid or other multiply connected surface and a pair of contrawound helical conductors wrapped upon such surface as a construction aid. Rectangular cross-section CTHAs may be employed. CTHAs having printed circuit conductors may also be employed, as well as a CTHA in the form of a conventional rigid dielectric printed circuit board (PCB).
Referring to FIG. 1, one type of CTHA 2, for example, employs a toroidal surface and two contrawound helical windings 4,6, which are fed with opposite currents in order that the magnetic flux of each helix reinforces the loop magnetic flux.
U.S. Pat. Nos. 4,622,558; and 4,751,515 discuss certain aspects of toroidal antennas as a technique for creating a compact antenna by replacing the conventional linear antenna with a self resonant toroidal structure that produces vertically polarized radiation that will propagate with lower losses when propagating over the earth. These patents initially discuss a monofilar toroidal helix as a building block for more complex directional antennas. Those antennas may include multiple conducting paths fed with signals whose relative phase is controlled either with external passive circuits or due to specific self resonant characteristics. In a general sense, the patents discuss the use of so called contrawound toroidal windings to provide multiple polarization.
U.S. Pat. No. 5,654,723 discloses antennas having various geometric shapes, such as a sphere. For example, if a sphere is small with respect to wavelength, then the current distribution is uniform. This provides the benefit of a spherical radiation pattern, which approaches the radiation pattern of an ideal isotropic radiator or point source, in order to project energy equally in all directions. Other geometric shapes may provide similar benefits. Contrawound windings are employed to cancel electric fields and leave a magnetic loop current. Thus, different modes of operation of CTHAs may be induced by varying the antennas"" geometric properties.
U.S. Pat. No. 5,709,832 discloses a printed monopole antenna including a PCB having a conductive trace formed on one side thereof.
U.S. Pat. No. 6,304,231 discloses an antenna embedded in a flexible circuit, which is mounted with adhesive on a planar member.
U.S. Pat. Nos. 5,173,715; and 5,521,610 disclose a flexible circuit comprising a pair of printed circuit antenna elements and a set of four printed circuit anchors, which are all disposed on one side of an insulating substrate. The proximity of the ends of the antenna elements to respective grounded anchors is such that some capacitive loading results. Preferably, such capacitive loading is, controlled and evenly matched in order to obtain an optimum hemispheric reception pattern. The antenna elements form orthogonal dipole antennas that are slightly shorter than one-quarter wavelength at the GPS L1 carrier frequency. See, also, U.S. Pat. No. 6,111,549.
U.S. Pat. No. 5,646,635 discloses an antenna including a non-conductive sheath or covering, which encloses an upper radiator of a radiator. That PCB radiator also includes a lower radiator, which is received by an elongated slot of a housing member. Both the upper and lower PCB radiators have conductive serpentine traces provided thereon in conventional fashion. The PCB radiators are flexible and are preferably comprised of a metallic conductor attached to a flexible substrate, for example, a copper conducting trace on a flexible polyamide substrate forming a common flexible circuitry material. The serpentine trace is selected to provide the options of inductance, capacitance and distributed capacity between traces in order to provide optimal matched conditions to the circuitry to which it is attached.
U.S. Pat. No. 6,069,592 discloses a cylindrical configuration into which a meander element and a flexible film carrier are shaped together. Alternatively, the flexible film carrier could be exchanged for another dielectric carrier, preferably having a cylindrical shape with some suitable cross-section, on which a meander conductor may also be applied or developed by a high precision technique, for example etching. Alternatively, two individual meander elements each have their own feed point to be coupled individually to circuitry of a telephone, possibly via an impedance matching circuit.
U.S. Pat. No. 6,320,550 discloses a Contrawound Helical Antenna.
There is room for improvement in transmitting and receiving contrawound antennas.
These and other needs are met by the present invention in which an electromagnetic antenna employs first and second contrawound helices on a flexible printed circuit board.
As one aspect of the invention, an electromagnetic antenna for a non-planar surface comprises: a flexible printed circuit board having at least three conductive levels, the flexible printed circuit board being adapted to conform to the non-planar surface, the flexible printed circuit board including a plurality of electrical connections between the conductive levels and a plurality of electrical traces on the conductive levels, the electrical connections and the electrical traces forming a first helix having a first helical pitch sense from a first node to a second node, and also forming a second helix having a second helical pitch sense, which is opposite from the first helical pitch sense, from a third node to a fourth node, the first and second helices being contrawound relative to each other; first and second signal terminals; and means for electrically connecting the signal terminals with at least one of the nodes.
The first node may be electrically connected to the fourth node and the second node may be electrically connected to the third node in order that the first and second helices form a single endless conductive path; and the means for electrically connecting may include a first electrical connection from the first signal terminal to the first node, and a second electrical connection from the second signal terminal to the third node.
The first node may be electrically connected to the second node and the third node may be electrically connected to the fourth node in order that the first and second helices form two endless conductive paths; and the means for electrically connecting may include a first electrical connection from the first signal terminal to the first node, and a second electrical connection from the second signal terminal to the third node.
The flexible printed circuit board may be adapted to conform to a surface of an aircraft, a vehicle, a water vessel, or an arcuate surface as the non-planar surface.
The flexible printed circuit board may be adapted for attachment to the non-planar surface, for partial wrapping about a closed surface as the non-planar surface, or for complete wrapping about a closed surface as the non-planar surface.
As another aspect of the invention, an electromagnetic antenna comprises: a flexible printed circuit board having at least three conductive levels, a first end and a second end, the first end being positioned proximate the second end to form a non-planar surface, the flexible printed circuit board including a plurality of electrical connections between the conductive levels and a plurality of electrical traces on the conductive levels, the electrical connections and the electrical traces forming a first helix having a first helical pitch sense from a first node to a second node, and also forming a second helix having a second helical pitch sense, which is opposite from the first helical pitch sense, from a third node to a fourth node, the first and second helices being contrawound relative to each other; first and second signal terminals; and means for electrically connecting the signal terminals with at least one of the nodes.
The first node may be electrically connected to the fourth node and the second node may be electrically connected to the third node in order that the first and second helices form a single endless conductive path; and the means for electrically connecting may include a first electrical connection from the first signal terminal to the first node, and a second electrical connection from the second signal terminal to the third node.
The first node may be electrically connected to the second node and the third node may be electrically connected to the fourth node in order that the first and second helices form two endless conductive paths; and the means for electrically connecting may include a first electrical connection from the first signal terminal to the first node, and a second electrical connection from the second signal terminal to the third node.
The non-planar surface may be a cylinder.
As another aspect of the invention, an electromagnetic antenna for a non-planar surface comprises: a flexible printed circuit board having at least three conductive levels, the flexible printed circuit board being adapted to conform to the non-planar surface, the flexible printed circuit board including a plurality of electrical connections between the conductive levels and a plurality of electrical traces on the conductive levels, the electrical connections and the electrical traces forming a first helix having a first helical pitch sense from a first node to a second node, and also forming a second helix having a second helical pitch sense, which is opposite from the first helical pitch sense, from a third node to a fourth node, the first and second helices being contrawound relative to each other; first and second signal terminals structured for transmitting or receiving an antenna signal; and means for electrically coupling the antenna signal to or from the first and second helices.
As another aspect of the invention, an electromagnetic antenna comprises: a flexible printed circuit board having at least three conductive levels, a first end and a second end, the first end being positioned proximate the second end to form a non-planar surface, the flexible printed circuit board including a plurality of electrical connections between the conductive levels and a plurality of electrical traces on the conductive levels, the electrical connections and the electrical traces forming a first helix having a first helical pitch sense from a first node to a second node, and also forming a second helix having a second helical pitch sense, which is opposite from the first helical pitch sense, from a third node to a fourth node, the first and second helices being contrawound relative to each other; first and second signal terminals structured for transmitting or receiving an antenna signal; and means for electrically coupling the antenna signal to or from the first and second helices.